1. Field of the Invention
The present invention relates to a printer and in particular to its platen structure.
2. Related Background Art
A typical printer generally comprises a recording sheet supplier for separately supplying a recording sheet stored therein (e.g., recording paper), a recording-sheet conveyance section composed of a conveyance roller for feeding the sheet sent separately into a recording area and its driven roller, a recording head for recording onto a recording sheet, a platen for at least supporting the back face of the site of a recording sheet corresponding to the recording area recorded by the recording head, and a discharge section for discharging the recording sheet on which recording has been completed.
The recording sheet supplied by a recording sheet supplier is held between a conveyance roller and its driven roller and is sent onto the platen corresponding to a recording area by the conveyance roller. And, on the recording sheet, one or several setup lines of image recording is made by means of a recording head. After repeating the recording sheet conveyance and the image recording of one or several lines in succession till the data sent from the host computer side comes to an end, a printer discharges the recording sheet to a tray.
In such printers, most platens are integratedly formed of a resin. By appropriately selecting the molding conditions such as smoothness of the surface, planarity of the smoothness or height of a rib installed protuberantly on the surface, a platen molded of a resin or an elastic member is capable of implementing high accuracy. Furthermore, lightening of the total weight can be achieved. Or, because of a high degree of freedom in shape, they are advantageous also in easily overcoming a problem that restrictions are imposed thereon such as positioning or fitting to the surrounding construction.
In an ink jet printer for discharging ink droplets to a recording sheet to make a record, for example, the platen in the recording area is generally broader in width than a recording sheet conveyed thereto, and with respect to the conveyance direction of recording sheets, the platen is most ideally constructed so as to be broader than the recording width by means of a recording head for all recording areas and as to keep a uniform distance between a recording sheet and the recording head. Besides, the surface of the platen for supporting the recording sheet conveyed thereto is mostly a smooth plane or is equipped with a plurality of rib-shaped objects with a smooth plane parallel to the conveyance direction of recording sheets provided thereon. By attaching and fixing such a platen to a given position of a chassis or the like of a printer body, the distance between a recording head section for discharging a recording liquid and a recording sheet is kept to a given interval or a given positional relation (e.g., a mutual positional relation such that the distance between the nearest site of a recording sheet to a recording head and the recording head is prevented from becoming inferior to a given value) and a high grade of image recording is formed.
FIG. 5 shows one example of the shape of a platen made by the resin molding. On the top face of the platen 50 corresponding to the recording area defined by the recording head section, a plurality of rib-shaped objects is formed in parallel with the conveyance direction of the recording sheets. The recording sheet conveyed is pressed to a top face of a rib 51 and placed so as to establish the surface position of the recording sheet by taking the rib height of the platen that supports a back face of the recording sheet as a reference. Taking the rib height of the platen as a reference makes it possible in an ink jet printer, for example, to maintain the distance between a recording sheet and the recording head to a given interval or a constant distance in a recording area and to make a more uniform image recording while avoiding the contact between a recording sheet and the recording head in all recording areas. At this time, in order to make a high grade image recording, high accuracy is required at the height of a sheet passing surface corresponding to the height reference of a recording sheet on the platen and the position thereof. The platen illustrated here is U-shaped with the rib-surface taken as the top face for the purpose of raising the rigidity so that it is affected as little as possible by warping or the like.
In some cases of molding a platen of a resin or an elastic member, however, a problem arises in that warping in the mold occurs on account of a lag of cooling time due to the internal stress or casting of a resin or the like. This is apt to occur mainly along the length of the platen in which rigidity becomes difficult to obtain. Especially, in some cases of a plurality of rib-shaped conveyance members provided on the top face of a platen in parallel to the conveyance direction of the recording sheets, on account of the internal stress of a resin during the cooling, the conveyance guides have mutually affected the occurrence of warp of the whole platen along the length of the platen also. Besides, when the width of the corresponding recording sheet is broadened and the length of a platen along the crossing direction of recording sheet conveyance is correspondingly increased, and further, with an increase in the recording area in the direction of recording sheet conveyance due to an increase in the number of nozzles of the recording head or the like, the amount of deformation due to warp was more likely to increase. To prevent such a problem, it was necessary to suppress the deformed amount of the platen to the minimum by taking such countermeasures as to fully perform the cooling during the molding or as to make the shape of the platen into a shape less subject to the internal stress of the resin as possible.
Besides, depending on characteristics of a platen material, the platen has been subjected to an aging change under influence of external environmental conditions such as temperature and humidity after its incorporation into a printer or warping or the like has occurred on account of even minute deformation in shape due to the weight of the platen itself.
It is one object of the present invention to provide a platen, whose deformations such as warp, in particular longitudinal warp, are least likely to occur, capable of maintaining a recording medium support plane, and formed by a plurality of recording medium support parts, at a more highly accurate planarity and a printer using the same.
It is another object of the present invention to provide a platen that does not bend on account of an internal stress occurring during the resin cooling or a lag of cooling time and a printer using the same.
It is another object of the present invention to provide a platen that is not subjected to aging change after being incorporated into the printer due to influence of external environmental conditions such as temperature or humidity depending on characteristics of a platen material and a printer using the same.
It is another object of the present invention to provide a platen used for a printer, whose longitudinal component is made of a rigid member and in which a plurality of recording support parts are respectively disposed independently in a direction crossing the length and a printer using the platen.